| Mercury is a kind of global contaminant, once emitted to the atmosphere, mercury can travels worldwide before deposits to ecosystems in either wet or dry form, thus can potential affect human health. Mercury content are elevated in high elevation mountain land by “elevation effect”, this made that kind of environment a potentially gathering place of mercury. Jiuzhaigou National Nature Reserve, Easten Tibet Plateau, is an important part of World Natural Heritage and Man and the Biosphere Programme, and also a typical example of subalpine environment. Studying the mercury distribution characteristics in different medias of this area, will provide basic data for further research about the distribution, transformation, and bio-activity of mercury in subalpine environment; Also will be meaningful for forecasting the longterm effects of airborne mercury in subalpine environment and can provide references for environmental protection policies making.Methods Stratified random sampling method was used, sample plots was set at different altitudes, then choose representative quadrats to collect soil, plant, litter samples. Leachates was collected by pre-embedded Lysimeters under different vegetations-covered area. Representative lakes were chosen to collect sediment core samples.Results The mean mercury contents of plants and litters in Jiuzhaigou subalpine environment are 0.044 mg/kg and 0.052mg/kg respectively. There are no significant mercury content difference in different species of plants(p=0.177), and also no significant altitude trends of mercury content in plants(p=0.874). The mean mercury content of soil is 0.161 mg/g, the result of ANOVA(p=0.061) shows that the difference of altitude doesn’t has a significant impact on the mercury content in soils. The mean mercury content of leachates is 22.579 mg/L, and leachates collected at coniferous forest covered sampling sites have significant higher mercury content than broadleaf forest covered sites(p=0.030). The mean mercury content of sediment is 0.036 mg/kg, there are significant differences of sediment mercury content between lakes(p<0.03), and also significant differences between different sampling sites in the same lake(p<0.042).The correlation between environmental factors and mercury content are different. The mercury content in soils are significantly positively related to organic matter content(p=0.05), and significantly negatively related to p H(p=0.01), while there’re no significant correlation between mercury content and TP or SO42-( p>0.446). DOC in leachates is positively related to mercury content(p=0.149), but can’t reach significance level. Except water inlet of Double Dragon Lake(p=0.530) and water outlet of Rhinoceros Lake(p=0.331), organic matter content in sediment are positively related to mercury content(p<0.048).On a century time scale, the mean mercury deposition flux rate in sediment is 0.009μg/m2/yr, and have obvious temporal and spatial patterns. The mercury deposition flux rate in sediment are significant different among different lakes(p<0.005), and the water inlet of Rhinoceros Lake has the highest mercury deposition flux rate at 0.103μg/m2/yr.Main conclusions Within the study spatial scale, mercury content in plants and soil don’t show a obvious spatial pattern; but mercury content in leachates under different vegetation-covered types has a obvious spatial trend. The p H and organic matter content in soil/sediment and DOC in leachate may have important effects on the transfer of Hg.The mercury content in sediment of Jiuzhaigou lakes have obvious temporal and spatial variations, mercury deposition flux rate is closely related to artificial disturbance. |
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